1,1&#39;-diaralkyl-4,4&#39;-carbocyanine salts



Patented Mar. 4, 1941 UNITED STATES IPATENT OFFICE 1,imnnALKYL-i,4'oAnBooYANINE sALTs Jersey Application November 20,l 1937, Serial No. 175,686

5 Claims.

This invention relates to new dyes and to photographic emulsions containing the same.

A number of cyanine dyes are known and vsome of these have been found to sensitize photographic emulsions in different useful manners. We have now found that if, in cyanine dyes which sensitize, at least one of the alkyl groups on the cyanine nitrogen atoms is an aralkyl group devoid of nitro groups, the sensitizing properties of the dyes are considerably altered so that from such dyes new and useful photographic emulsions can be prepared. We have found that the alteration in sensitizing properties is most pronounced in sensitizing dyes of the carbocyanine, dicarbocyanine, tricarbocyanine, tetracarbocyanine and pentacarbocyanine groups.

It is accordingly among the objects of our invention to provide new cyanine dyes. in which at least one of the alkyl groups on the cyanine nitrogen atoms is an aralkyl group devoid of nitro groups. A further object is to provide a process for preparing such dyes. A further object is to provide intermediate compounds for the preparation of such dyes and a process for the prep- 25 aration of such intermediatecompounds. A still further object is to provide photographic emulsions sensitized in a novel and useful manner. A still further object is to provide a photographic element containing such sensitized photographic emulsions. Stil1 other more specific objects and advantages will become apparent hereinafter.

Our new dyes can be prepared utilizing cyclammonium aralkyl quaternary salts which can be prepared as hereinafter set forth. Cyclammonium aralkyl quaternary salts can be prepared for example by reacting a heterocyclic nitrogen base with aralkyl halides. We have found the aralkyl bromides and iodides are advantageously employed. Heat accelerates the formation of our new quaternary salts. Diluents can be employed in the reaction mixture, although they are not essential. The aralkyl quaternary halides can be converted into the less soluble quaternary salts, e. g., the alalkyl bromides into iodides or perchlorates, by treating solutions of the quaternary halides with solutions of soluble iodides or perchlorates.

While our method of obtaining aralkyl quaternary salts is subject to variation, particularly as respects the nature and quantity of heterocyclic nitrogen base employed, the nature and quantity of aralkyl halide employed, the temperatures employed, the nature and quantity of aralkyl halide employed, the nature and quantity of diluent employed, if any, the time of reaction employed and (c1. 26o-24o) the method of isolation and purification of the quaternary salts, the following examples will serve to illustrate the mode of obtaining our new qua.- ternary salts. These examples are not intended to limit our invention.

5.1 g. (1 mol.) of 2-iodoquinoline and 4.36 g. (1 mol.) of benzyl iodide were heated together at about '0l C. for about one week. The crude quaternary salt was recrystallized from nitromethane andobtained as yellowish crystals melting at 190 to 192 C. with decomposition.

EXAMPLE 2.-1-methylbenzothiaeole benzobromz'de '7.5 g. (1 mol.) of l-methylbenzothiazole and 8.6 g. (1 mol.) of benzyl bromide were heated together in about 25 cc. of dry chloroform at the refluxing temperature for about hours. The crude quaternary bromide separated from the reaction mixture. It was recrystallized from methyl alcohol and obtained as cream colored crystals melting at 231 to 232 C. with decomposition.

EXAMPLE 3.-1-methylbeneothiaeole benezodz'de 14 g 4 (1 mol.) of 1methylbenzothiazole benzobromide were dissolved in about cc. of hot water andtreated with cc. of an aqueous solution containing 15 g. (2 mol.) of potassium iodide. The crude quaternary iodide separated from the cooled reaction mixture. It was thrice recrystallized from methyl alcohol and obtained as cream colored crystals melting at 207 to 210 C. with decomposition.

10g. (1 mol.) of quinaldine and 12 g. (1 mol.) of benzyl bromide were heated together at about 100 C. for about 15 hours. The cooled solid reaction mass was broken up and ground with acetone. The crude solid quaternary bromide was dissolved in about 10 cc, of hot methyl alcohol. The solution was filtered and .the quaternary bromide precipitated therefrom by adding diethyl ether. The so precipitated bromide was dissolved in about 20cc. of hot water and treated with a concentrated aqueous solution of potassium iodide containing 3.3 g. (2 mol.) of potassium iodide. The crude quaternary iodide'separa-ted from the reaction mixture. It was twice recrystallized from hot water, decolorizing the solution of activated charcoal, and obtained as orange-yellow needles melting at 220 to 221 C. with decomposition.

- toluenesulfonate.

EXAMPLE 5.-Lepdz'ne benez'odde 4.8 g. (1 mol.) of lepsidine and 5.7 g. (1 mol.) of benzyl bromide were heated together in about 10 cc. of dry chloroform at the refluxing temperature for about 2 days. The crude quaternary bromide was iiltered off and dissolved in about 30 cc. of hot water. The aqueous solution of the quaternary bromide lwas treated with 10 oc. of an aqueous solution of potassium iodide containing 11 g. (2 mol.) of potassium iodide. The crude Quaternary iodide separated from the reaction mixture and was thrice recrystallized from methyl alcohol. It was obtained as yellow crystals melting at 161 to 163 C. with decomposition.

EXAMPLE 6.-Quinoline lbenzz'odiole 12.9 g. (1 mol.) of quinoline and 17.1 g. (1 mol.) of benzyl bromide were heated together at about C. for about 4 hours. action mass was dissolved in about 40 cc. of methyl alcohol and treated with a concentrated aqueous solution of potassium iodide containing 28.6 g. of potassium iodide. 'Ihe benziodideprecipitated as yellow crystals melting at to 166 C. with decomposition.4

28.6 g. (1 mol.) of quinaldine and 37.0 g. (1v mol.) of lS-ethylbromide were heated together at about 100 C. for about 6 days. The solid dark mass was dissolved inhot `water and treated with a concentrated aqueous solution of potassium iodide containing 32 g. of potassium iodide. The quaternary iodide .precipitated as brownish yellow crystals. It was recrystallized from water and obtainedas yellowish crystals melting at to 191 C. with decomposition. l

In a manner similar to that illustrated inthe above eight examples, aralkyl quaternary salts of 1 methylbenzoxazole, a methylnaphthothiazoles, ,u methylnaphthoxazoles," 2 methyl-4- phenylthiazole, 1 methylbenzoselenazole, 2- methyl-4-phenyloxazole, 2 methyl 4 phenylselenazole, 2,4-dirnethylthiazole, Z-phenylthioquinoline,l 2-methylthiobenzothiazole, 2-butylthiobenzothiazole, aand y-picolines or the like can be prepared. We have illustrated particularly the formation of aralkyl -quaternary salts fromr quinoline, and b enzothiazvole bases since nuclei corresponding to these bases are found in a number of goodsensitizing dyes. Still other aralkyl' quaternary salts of heterocyclic nitrogen bases can be prepared by treating the heterocyclic nitrogen bases, as set forth in the foregoing examples, with esters, such as -phenylethyl toluenesulfonate or I7,1-phenyl--n-propyl Such esters can be prepared, 'for example, from -phenylethyland y-phenyln-propylalcohols-by themethod for preparing toluenesulfonate esters described by Fldi in Berichte der deutschen chemischen Gesellschaft,

The solid re-` aesasm vol. 53, page 1836 (1920), for example. However, we have found that our new dyes are advantageously prepared employing the aralkyl quaternary halides. While we have illustrated particularly the formation of aralkyl quaternary salts from unsubstituted heterocyclic nitrogen bases such as quinoline and benzothiazole, heterocyclic nitrogen bases, particularly those containing a benzene nucleus containing ordinary simple substituents particularly in the benzene nuclei can also be converted into aralkyl quaternary salts as set forth above. For example, heterocyclic nitrogenl bases containing substituents such as dialkylamino, alkyl, alkoxy or acylamino groups on halogen atoms can be converted into Varalkyl quaternary salts.

Instead of benzyl iodide in the above examples, chlorobenzyl,

vmethylbenzyl or methoxybenzyl iodide, for example, can -be employed.

Having set forth the manner of obtaining the intermediates necessary to the preparationof our new dyes, a number of examples of the preparation of various cyanine dyes `of sensitizing types from such intermediates are hereinafter set forth. j

Our new intermediates can beemployed in preparing simple cyanine dyes, i. e. cyanine dyes containing a single methenyl group between two EXAMPLE 9 1'-benzyZ-Z-ethylthia-Z-cydnne iodide 2.62 g. (1 mol.) of l-methylben'zothiazole ethop-toluene-sulfonateand 3.55v g. (1 mol.) of 2- iodoquinoline benzio-dide were heated together in 15 cc. of absolute ethyl alcohol containing 2.2 cc. (2.1 mol.) of triethylamine at the reuxing temperature for about 20 minutes. The dye separated from the cooled reaction mixture. The

dye was twice recrystallized from methyl alcohol and obtained as dark crystals having a bluish reflex. It gave an orange colored methyl alcohol solution and melted at 243 to 245 C. with de- The dye has rthe composition. following formula I Employing 1 methylbenzothiazole metho p toluenesulfonate instead of eth0, lf-benzyl-Z- methylthia-2cyanine iodide can beobtained as reddish-orange crystals with a brightv reflex and melting at 256 to 258C. with decomposition.

EXAMPLE 10.-2l1eneyl-1 -ethylthz'd-Z -cyanine iodide 3.67 g. (1 mol.) of l-methylbenzothiazole ethiodde and 4.1 g. (1 mol.) .of 2-iodoquinoline benziodide were heated together in 35 cc. of absolute ethyl alcohol containing 3.0 cc. (2.1'mo-1.) of triethylamine at the refluXing temperature for about twenty minutes. The dye separated from the cooled reaction mixture. The dye was twice recrystallized from methyl alcohol and obtained as an orange powder which gave a brownishorange methyl alcohol solution and melted at 256 to 258 C. The dye has the following Employing 2-iodoquinoline methiodide instead of the ethiodide, 2-benzyl-1-methylthia-2'cyanine iodide can be obtained as dark crystals having a green reflex, giving a reddish-orange methyl alcoholic solution and melting at 260 to 261 C. with decomposition.

EXAMPLE 12.-1'-benzyl-Z-ethylthid-4'-cycm'ine iodide 3.05 g. (l mol.) of l-methylbenzothiazole ethiodide and 6.94 g. (2 mol.) of quinoline ethiodide were heated together in 15 co. of absolute ethyl alcohol containing 1.4 g. (2 mol.) of 85% potassium hydroxide at the refluxing temperature for about twenty minutes. The dye separated from the cooled reaction mixture. It was twice recrystallized from methyl alcohol and obtained as orange-red crystals giving a, reddish-orange methyl alcoholic solution and melting at 268.to

autes.

270 C. with decomposition. The dye has the following formula:

lLC=CH-(:'y 2l\ 1/ I 32H5 Employing l-,methylbenzothiazole benziodide instead of ethiodide and quinoline ethiodide instead of benziodide, 2-benzyl-1ethylthia4 cyanine iodide can be similarly obtained as fine orange-red crystals melting 4at 280 to 282 C. with decomposition.

EXAMPLE 1 3.-1 ,2- dz'beneylthia-4 -cyanine iodide 3.67 g. (1 mol.) of 1methylbenzothiazole benziodideland6-94 g. (2 mol.) of quinoline benziodide were heated together'in` 25 cc. of absolute ethyl alcohol containing 1.4 g. (2 mol.) of 85% potassium hydroxide at the --reuxing :temperature for about twenty minutes. The dye separated from the cooled reaction mixture. The dye Was twice recrystallized from methyl alcohol and obtained as orange-red crystals which gave a reddish-orange methyl alcoholic-solution and melted at 265 to 266 C. with decomposition. The dye has the following'formula:

1.2 g. (1 mol.) of `quinaldine benziodide and 1.58 g. (l mol.) of 2-iodoquinoline benziodide were heated together in 10 co. of absolute ethyl alcohol containing 1.0 cc. (2.1 mol.) of triethylamine at the refluxing temperature for about twenty minutes. The dye separated from the cooled reaction mixture. It was recrystallized from. methyl alcohol and obtained as reddishbrown flakes having a golden reflex and giving a reddish-orange methyl alcoholic solution. The

4dye melted at 238 to 240'C.'with decomposition.

The dye has'the following formula:

. EXAMPLE 15.--1-benzylf1'-ethyl-2,2cyanine 'iodide 1.5 g. (1 mol.) of quinaldine ethiodide and 2.37 i

g. (1 mol.) of 2-iodoquinolinebenziodide were heated together in 10 cc. absolut-e ethyl alcohol containing 1.5 .cc. (2.1 mol.) of triethylamineat thereiluxing temperature for.. about .twenty min- Theidye separated-"from the reactionzmix- ,orange methyl alcoholic solution.

By treating 3.6 g. of quinaldine benziodide and 3.91 g. of 2iodoquinoline methio'dide as set forth in this example, l-benzyl-1-methyl2,2cyanine iodide can be prepared.- This dye was obtained as large reddish-brown crystals having a green reex and giving a reddish-orange methyl alcoholic solution. It melted at 220 to 222 C. with decomposition.

EXAMPLE 16.--1-benayZ-1-methyi-2,4 cyanine odid'o 2.14 g. (1 mol.) of lepidine methiodide and 3.55 g. (1 mol.) of 2-iodoquinoline benziodide were heated together in absolute ethyl alcohol containing 2'.2 cc. (2.1 mol.) of triethylamine at therefluxing temperature for about twenty minutes. The dye separated from the reaction mixture upon chilling. After two recrystallizations from methyl alcohol, the dye was obtained as large, long, green, lustrous crystals which gave a bluishred methyl alcoholic solution. The dye melted at 249 to 251 C. with decomposition. The dye has the following formula:

By treating 3.61 g..of lepidine benzodide and 3.97 g. of 2-iodoquinoline methiodide as described in this example, 1benzyl1methyl-2,4'cyanine iodide can be obtained as green needles having a bright reflex and giving a bluish-red methyl alcoholic solution. This dye melts at 266 to 268 C. with decomposition.

Likewise, by treating 2.25 g. of lepidine ethiodide and 3.55 g. of 2-iodoquinoline benziodide in the manner set forth in this example, l-benzo-lethyl-2,4'cyanine iodide can be prepared. This dye, after two recrystallizations from methyl alcohol, was obtained as lustrous green crystals giving a bluish-red methyl alcoholic solution and melting at 239 to 242 C'. with decomposition.

By treating 0.9 g. of lepidine benziodide and 1.03 g. of 2-iodoquinoline ethiodide as set forth in this example, 1benzyl1ethyl 2,4' cyanine iodide can be obtained. However, it is necessary to add diethyl ether to the reaction mixture after heating for twenty minutes and then cooling in order to precipitate the dye. After recrystallization from methyl alcohol the dye was obtained as minute dark crystals having a bright reilex and giving a crimson methyl alcoholic solution. The dye melted at 263 to 264 C. with decomposition.

EXAMPLE 18.-1-benzyl-1-methyl-4,4' v cyanine iodide 3.61 g. (l mol.) of lepidine benziodide and 5.42 g.' (2 mol.) of quinoline methiodide were heated together in 20 cc. of absolute ethyl alcohol containing 1.4 g. (2 mol.) of 85% potassium hydroxide at the refluxing temperature for about twenty minutes. The dye separated from the cooled reaction mixture. After two recrystallizations from methyl alcohol, the dye was obtained as minute light green crystals having a shining reilex and giving a blue methyl alcoholic solution.. The dye melted at 266 to 267 C. with decomposition. The dye has the following formula:

By treating 3.61 g. of lepidine benziodide and 5.7 g. of quinoline ethiodide as set forth in this example, l-ethyl-1'-benZyl-4,4cyanine iodide can be obtained. However, it is necessary to chill the reaction mixture in order to cause separation of the dye. After two recrystallizations from methyl alcohol, the dye was obtained as grayish-greenr crystals having a bright reex and giving a blue methyl alcoholic solution. The dye melted at 234 to 236 C. with decomposition.

EXAMPLE 19.-1,1-dibenzyZ4,4'-cyanine iodide 3.61 g. (1 mol.) of lepidine benziodide and 6.94 g. (2 mol. )of quinoline benziodide were heatedtogether in absolute. ethyl alcohol cc.) containing 1.4 g. (2 mol.) of 85% potassium hydroxide at the rei-luxing temperature for about twenty minutes. 'The dye separatedv from the reaction mix- -tureV upon chilling. After two recrystallizations from methyl alcohol, the dye was obtained as large, lustrous green crystals having a bronze reflexand giving a blue methyl alcoholic solution.

The dye melted at 183 to 187 C. with decomposition and has the following formula:

pinkish-red solution'in methyl alcohol. The dye melted at 250 to'25 1 C. with decomposition.

EXAMPLE 20.-1 '-ethyl-.Z- (-phenylethyl) -thia- Z'cyam'ne iodide By treating 3.81 g. of 1-methylbenzothiazole -phenyl-ethiodide and 3.97 g. of 2-.iodoquinoline ethiodide as set forth in this example, 1- methyl- 2 (-phenylethyl) -tha-2'cyanine iodide can be prepared. After recrystallization from methyl alcohol, the dye was obtained as brown crystals melting at 260 to 261 C. with decomposition. The dye gave an orange methyl alcoholic solution.

3.75 g. (1 mol.) of quinaldine -phenylethiodide and 4.1 g. (1 mol.) of 2-iodoquinoline ethiodide were heated together in about cc. of absolute ethyl alcohol containing 2.9 cc. (2.1 mol.) of trithylamine at the refluxing temperature for about twenty minutes. Diethyl ether was added to the cooled reaction mixture to precipitate the dye. After recrystallization from methyl alcohol, the dye was obtained as red-brown needles having a bright greenish-bronze reex and giving a pinkish-red methyl alcoholic solution. The dye melted at 149 to 151 C'. with decomposition.

By treating 3.75 g. of quinaldine -phenylethiodide and 3.97 g. of 2-iodoquinoline methiodide as set forth in this example, 1methy11(/8 phenylethyl)-2,2'cyanine iodide can be prepared. However, it is not necessary to add diethyl ether to the cooled reaction mixture, as the dye separates even While th-e reaction mixture is hot. After recrystallization from methyl alcohol, the dye was obtained as small brownish crystals having a metallic green reflex and giving a EXAMPLE 22.- L- ethyl-J -phenylethyl) `2,4

cyamne. iodide 1.88 g. (l mol.) of lepidine Ili-phenylethiodide and 2.06 g. (l mol.) of 2-iodoquinoline ethiodide were heated together in cc. of absolute ethyl alcohol containing 1.46 cc. (2.1 mol.) of triethyl-y amine at the refluxing temperature for about twenty minutes. The dye separated from'the reaction mixture upon chilling. After recrys' tallization from methyl alcohol, the dye Was obtained as greenish-bronze crystals melting at 225 to 227 C. with decomposition, and giving a crimson methyl alcoholic solution. The dye has the following formula:

1 sua \I (52H5 In the above examples of the preparation of simple cyanine dyes, ethyl alcohol has been employed exclusively as a diluent in the reaction mixture because the reactions proceed well at the refluxing temperature of the alcohol, i. e. from 70 to 80 C. Other diluents can be employed, e. grmethyl alcohol or n-propyl alcohol are satisfactory. The reactions can be carried out with no diluent, though it is diicult to isolate the dyes under such conditions.

In the above examples of the preparation of 2cyanine, i. e. pseudocyanine, dyes the basic condensing agent employed has been exclusively triethylamine. Strong tertiary organic bases, i. e. tertiary organic bases whose aqueous solutions have dissociation constants substantially greater than that of an aqueous solution of pyridine, are particularly advantageously ernployed, e. g. N-methylpiperidine, triethanolamine, tributylamine and triethylamine. Other basic condensing agents can be employed. Alkali metal carbonates are particularly eicacious. Pyridine, sodium hydroxide or sodium perborate can also be used. In the preparation of 4- cyanine (isocyanine) dyes, the alkali hydroxides, such as potassium and sodium hydroxide, are advantageously employed.

2cyanine dyes can also be prepared by treating aralkyl Quaternary salts of 2-phenylmercaptoquinoline with cyclammonium Quaternary salts containing a reactive methyl group, such as l-methylbenzothiazole, quinaline, a-picoline, Z-methyl-4-phenylthiazole or 2-methyl-4-phenyloxazole for example, laccording to the process given in the above examples.

Simple thiacyanines having the following formula:

I N/ \N i R/ \X wherein R and R' represent alkyl groups, but at least one of R and R is an aralkyl group and X represents an acid radical, can be prepared by treating 1-methylmercaptobenzothiazole aralkyl quaternary salts with l-methylbenzothiazole Quaternary salts according to the process of the above examples. Simple oxaand selenacyanines can be similarly prepared.

2,2'dibenzylthiacyanine iodide was obtained in the form of yellow crystals giving a yellow methyl alcoholic solution and melting at 265 to 266 C. with decomposition after recrystallization from methyl alcohol. This substance is also formed during the preparation of 2-benzyl-1ethylthia 2"-,cyanine iodide (see Example 11 above). The thiacyanine is more soluble in methyl alcohol and can accordingly be separated from the 2cyanine by fractional crystallization.

Our new intermediates can be employed to pre'- pare carbocyanine dyes, i. e cyanine dyes containing a trimethenyl 4'chain between two heterocyclic nuclei, such as 2,2carbocyanines, 2,4carbo cyanines, 4,4carbocyanines, thia-2'carbocya nines, oxa-2 carbocyanines, thiazolo2carbo cyanines, selenazolo-2'carb0cyanines, thia-4- oarbocyanines, selena4carbocyanines, Oxa-4'- carbocyanines, thiacarbocyannes, dibenzothiacarbocyanines, oxacarbocyanines, dibenzoxacarbocyanines, selenacarbocyanines, oxathiacarbocyanines, oxabenzothiacarbocyanines, benzoxathia# carbocyanines, thiazolocarbocyanines, thiathiadark green crystals havinga greenish-bronze re#` flex and giving a bluish-red methyl alcoholic solution. The dye melted at 268 to 269 C. with decomposition and has the following formula:

CH. CH2 Br EXAMPLE 25.--1 ,1 -dibena'yl- 4,4 -carbocyanine iodide f i 7.2 g. (2 mol.) of lepidine benziodide and 5cc.,v

(3 mol.) of ethyl orthoformate were heatedtof gether in 30 ce. of pyridine at the refluxing tem-k perature for about three hours.

rated from the cooled` reaction mixture. The

product which separated contained much -un-y It was carefully ex.

changed starting material. y tracted with methyl alcohol. The extract yielded the pure dye in the form of greenish-bronze nee` zolocarbocyanines and the like. The following examples are illustrative of the manner of obtaining our new carbocyanine dyes from our new quaternary salts. `These examples are not intended to limit our invention.

reex and giving a bluish-red methyl alcoholic.y

solution. The dye melted at 246 to 247 C. with decomposition and hasthe following formula:

EXAMPLE 24.-1 ,1 -dibenzyl-2,2 -cdrlaocyanine bromide 6.28 g. 2 m01.) of quinaldine berizobromiae and 4.95 cc. (3 mol.) of ethyl orthoformate were heated together in 15 cc. of pyridine for about four hours at the refluxing temperature. The dye was precipitated by adding diethyl ether to the cooled reaction mixture. It was recrystallized from methyl alcohol and obtained as minute 3.34 g. (2 mol.) of l-methylbenzothiazole phenylethobromide and 2.2 g. (3 mol.) of ethyl orthoformate were heated together in 15 ccrof pyridine for about twenty-five minutesat the rcfluxing temperature. A .concentrated aqueous solution of potassium iodide was added tothel cooled reaction mixture to precipitate the dye asv the dye-iodide.

lution. The dye melted at 245 to 248 C. with decomposition and has the following formula:

6.56 g. (2 mol.) fof quinaldine -phenylethobromide and 4.95 cc. (3 mol.) of ethyl orthoformate were heated together in 15 cc. of pyridine at the reiiuxing temperature for about four hours. Diethyl ether wasadded to the'cooled re;- action mixture to precipitaterthe dye. twice recrystallized from methyl alcohol Iandobtained as dark prism-s with a bright greenish-y bronze reex which gave a reddish-blue methyl alcoholic solution. The dye mel-ted at 243 to 246-"` C. with decomposition.

The dye sepa- It was recrystallized fromA methyl alcohol and'obtained as brassy crystals` which gave a bluish-crimson methyl alcoholic so-r lIt was` 7 .5 g. (2 mol.) of lepidine -phenylethiodide and 4.95 cc. (3 mol.) of ethyl orthoformate were heated together in 15 cc. of pyridine at the refluxing temperature for about four hours. The dye separated from the cooled reaction mixture. It was recrystallized from methyl alcohol :and obtained as dark needles having a bright brassy reilex and giving a greenish-blue methyl alcoholic solution.

In the above examples the pyridine functions both as a basic condensing agentand as `a diluent. Pyridine is a particular-ly eiiicacious condensing agent. Other diluents can be added to the reaction mixture. tageously carried out at about the reuxing .temperature of pyridine. In a manner similar to that illustrated in the above examples, dibenzothiacarbocyanines, oxacarbocyanines, selenaoarbocyanines, thiazolocarbocyanines :and thiazolinocarbocyanines containing aralkyl groups can lbe prepared. In the above examples instead 4of employing ethyl orthoformate, other esters of ortho formic acid can be used. Likewise, ethyl orthoacetate, ethyl orthopropionate and ethyl orthobenzoate can be employed in the above examples instead of ethyl orthoformate. Using these latter esters, -carbocyanin-e dyes containing a substituent :at .the central carbon atom of the trimethenyl chain can be prepared.

Unsymmetrical carbocyanine dyes containing aralkyl groups can be prepared by rst condensing a cyclammonium aralkyl quaternary salt containing'a reactive methyl group, advantageously an aralkiodide, wi-th diphenylforrnamidine, advantageously in the presence of an organic acid anhydride, such as acetic anhydride. The resulting condensation product can then be condensed with a different cyclammonium aralkyl quaternary salt containing a reactive methyl group, again advantageously an aralkiodide, in the presence of a basic condensing agent, advantageously a strong organic base, such as triethylamine or piperidine for example. In such .a manner, 2,2- dibenzyloxathiacarbocyanine iodide can be prepared for example.

(ln-symmetrical carbocyanine dyes containing at least one aralkyl group on the cyanine nitrogen atoms and having an alkyl group, particularly one of the ordinary yalkyl groups, such as methyl or ethyl, on the central carbon atom of the 'ftrimethenyl chain can be prepared as illustrated for the dye having the following formula:

To prepare this dye, Z-methyl--naphthothiazol benziodide is reacted with acetyl chloride in the presence of pyridine to give 2-acetylmethylene-1-benzyl--naphthothiazoline. The naphthothiazoline is then condensed with l-methylbenzoxazole benziodide in the presence of a waterbinding agent, such as acetic -or propionic anhydride.

Dcarbocyanine dyescontaining aralkyl groups The reactions are advanon at least one of the cyanine nitrogen atoms can be prepared by first condensing la cyclammonium aralkyl quaternary salt containing a reactive methyl group, advantageously .an aralkiodide wi-th -.anilinoacrolein anil hydrochloride, in the presence of sodium ,acetate and acetic anhydride. The condensation product can then be condensed with `the same or a diierent cyclammonium aralkyl Quaternary salts containing .a reactive methyl group, in the presence of a basic condensing agent, advantageously a strong organic base, such as triethylamine. In such a manner 2,2dibenzylthiadicarbocyanine iodide can be prepared.

'Iricarbocyanine dyes containing aralkyl groups on at least one of the cyanine nitrogen atoms can be prepared as illustrated in the following examples. These examples are not intended to limit our invention.

EXAMPLE 29 .-2,2 -dibenzylthiatricarbocyanme iodide 7.34g. (2 mol.) of l-methylbenzothiazole benziodide and 2.85 g. (1 mol.) of glutaconic `aldehyde dianilide hydrochloride were dispersed in about 400 cc. absolute ethyl alcohol. To the chilledy dispersion, 1.7 g. (2 mol.) of piperidine were added. The whole was then allowed to stan-d in an ice-box for about twenty-four hours. The dye had separated from the reaction mixture. It was twice :recrystallized from methyl alcohol and obtained as r-osettes of green crystals which gave a blue methyl alcoholic solution. The dye melted at 202 to 204 C. with decomposition. It has the following formula:

.EXAMPLE 30.-2,2di- (-phenyletzyl) -thiatrzcarhocyanine iodide 2.23 g. (2 mol.) of l-methylbenzothiazole phenylethobromide and 0.95 g. (1 mol.) of glutaconic aldehyde dianilide hydrochloride were dispersed in about 10 ec. of absolute ethyl alcohol. To the dispersion, 0.57 g. (2 mol.) of piperidine were added and the mixture was allowed to stand in an ice-box for about twelve hours. The dye separated from the reaction mixture. It was recrystallized from methyl alcohol and obtained as dark needles having a coppery reflex and giving a blue methyl alcoholic solution. It melted at to 193 C. with decomposition.

In a manner similar to that illustrated in the above two examples, 2,2-, selena-, dibenzothia, thiazolino, 4,4-, and thiazolotricarbocyanine dyes in which the :alkyl groups on the cyanine nitrogen atoms are aralkyl groups can be prepared. Instead of piperidine in the above two examples, other strong organic bases can be employed, for example, triethylamine, tributylamine or diethylamine,

Our new aralkyl Quaternary salts can be employed'to prepare tetraand pentacarbocyanine dyes. Our new cyclamrnonium aralkyl quaternary saltscontaining a reactive methyl group, such as l-methylbenzothiazole benziodide or phenylethiodide or a-niethylnaphthothiazole benziodide or ,B-phenylethiodide for example, can

be condensed with 4acyloxy-Aft-heptadiene-y 1,7-dial ditetrahydroquinolide perchlorate or 4- acyloxy-A351"-nonatriene1,9-dial ditetrahydroquinolide perchlorate, in the presence of pyridine or piperidine or a mixture of the two, to give tetriaand pentacarbocyanines respectively.

Our new cyclammonium aralkyl quaternary saltsl containing a reactive methyl group can be condensed with aldehydes, such as dialkylaminobenzaldehydes, dialkylaminocinnamaldehydes or the like to give dyes. The following examples are illustrative, but are not intended to limit our invention.

EXAMPLE 31.-p-diethylaminostyrylbeneothiaeole benzzodz'de EXAMPLE 32.-p-dietylamnostyrylbenzothiaaole -phenylethiodide 3.81 g. (1 mol.) of l-methylbenzothiazole phenylethiodide and 1.77 g. (1 mol.) of p-diethylaminobenzaldehyde were heated together in 15 cc. of absolute ethyl alcohol containing four ,v drops of piperidine at the refluxing temperature for about four hours. The dye separated from the cooled reaction mixture. It was recrystallized from methyl alcohol and obtained as dark blue crystals having a light blue reiiex and giving a bluish-red methyl alcoholic solution. It melted at 261 to 263 C. with decomposition. It has the following formula:

In a manner similar to that illustrated in the above two examples, other of our cyclammonium .aralkyl Quaternary salts, containing a reactive methyl group, such as those set forth in and under Examples 2, 3, 4, 5, 7 and 8, can be condensed with dialkylamino benzaldehydes or .cinnamaldehydes to give dyes. The piperidine employed in the above two examples does not act as a basic condensing agent to bind elements of ac id. Rather, in the above two examples the piperidine acts as a catalyst accelerating the splitting out of `water from the cyclammonium aralkyl quaternary salt and the aldehyde.

Our new dyes sensitize photographic emulsions in .a novel and useful manner.` Our invention is particularly directed to the customarily employed silver halide especially the silver chloride and'bromide emulsions, which may containl other salts which may be light sensitive. Our invention is further particularly directed to. the customarily employed gelatin emulsions. I-Iowever, the gelatin can` be replaced with any other` carrier which has substantially no deleterious eiect on the light-sensitive materials, e. g. with a cellulose derivative or a resin.

In the preparation of photographic emulsions sensitized Withvour new dyes, it is only necessary to thoroughly disperse a small amount of our dyes in an ordinary photographic emulsion. The suitable and most economical concentration for any given emulsion will be apparent to those skilled in the art upon making the ordinary tests and observations customarily used inthe art of emulsion making. To. prepare a gelatinosilver-halide emulsion the following procedure is satisfactory: A quantity of the dye is dissolved in a suitable solvent, for example methyl alcoholv or acetone', advantageously the former, and a volume of this solution (which may be diluted with water) containing fromv to 100 mg.

of dye is slowly added to about 1000 cc. of an ordinary lowable gelatino-silver-halide emulsionL with stirring. The dye is thoroughly incorporated. With the more powerful of our new-y sensitizing dyes, to 20 mg. of dye per 1000r cc. of emulsion will suice to produce maximum sensitizing effects with the ordinary gelatino-silver-halide emulsion.

The above statements are only illustrative andV are vnot lto lbe understood as limiting our invention in any sense as it will be apparent rthat these dyes can be incorporated by other methods in many of the photographic emulsions cus-A claims are intended to cover any combination ofl our new dyes with a photographic emulsion.

whereby the dyes exert a sensitizing effect upon the emulsion as well as a photographic element comprising a support, ordinarily transparent, upon which the light-sensitive emulsion is'coated or spread and permitted to set or dry.

The accompanying drawing4 is fby way of i1- lustration and is offered primarily to show the range of sensitivity of representative members of our longer chain dyes. Each gure of the drawing is a` diagrammatic reproduction of a. spectrogram showing the sensitivity of an ordinary gelatino-silver-bromide emulsion containing one of our new dyes. In Fig. 1 the curve represents the sensitivity of an ordinary gelatino-silver-bromide emulsion containing 2,2di benzylthiacarbocyanine iodide. In Fig. 2 the curve represents an ordinary gelatino-silverbromide emulsion containing 2,2di(phenyl ethyl) -thiacarbocyanine iodide. In Fig. 3 the curve represents the sensitivity of an ordinary gelatino-silver-ibromide emulsion containing 1,1-

dibenzyl-4,4-acarbocyanine iodide. In Fig. 4 the curve represents the sensitivity of an ordinary gelatino-silver-bromide emulsion containing-1,1- di- (-phenylethyl) -4,4.carbocyanine iodide, In

Fig. 5 the curve represents the sensitivity of an ordinary gelatinofsilver-bromide emulsion condibenzyl4,4carbocyanne iodide which is formulated as follows:

taining 2,2'dibenzylthiatricarbocyanine iodide.

Of our new dyes, the 1,1dibenzyl4,4car bocyanine dyes are particularly outstanding in their sensitizing power and photographic emulsions sensitized therewith are of particular utility. The 1,1'-dioenzyl-LA-carbocyanine dyes sensitize emulsions more strongly than any 4,4- carboeyanine dyes known heretofore. Still further examples of our new emulsions could be given, but the foregoing will serve to teach those skilled in the art the principles of sensitizing emulsions with our new dyes. The illustrations have been conned to dyes of the longer chain types since it is this group of our dyes which is of the greatest utility in sensitizing emulsions.

In the specification and claims, by the term cyanine nitrogen atoms we mean the two nitrogen atoms essential to the cyanine dye chromophor, i. e. the two nitrogen atoms, the

'one tervalent and the other quinquevalent,

which are linked together by a conjugated carbon chain. For example, in a dye such as 1,1'-

there are two nitrogen atoms (the cyanine nitrogen atoms) linked together by a conjugated chain.

What we claim as our invention and desire to be secured by Letters Patent of the United States 1s:

l. A 1,1'diaralky14,4'-carbocyanine salt in which the `aralkyl groups are devoid of nitro groups, the aryl nucleus in each of said aralkyl groups being a single ring nucleus of the benzene series.

2. A 1,1'diaralkyl4,4'-carbocyanine halide in which the aralkyl groups are devoid of nitro groups, the aryl nucleus in each of said aralkyl groups being a single ring nucleus of the benzene series.

5. A 1,1'-dibenzyl-4,4'-carbocyanine halide. 

